1. Field of The Invention
The present invention relates generally to a printer such as a laser, sublimation type color video printer for making a thermal imprint of still video or television images etc., on photographic paper using sublimation type dyes, or the like.
2. Description of The Related Art
Sublimation type printers have been proposed for applications requiring impression of video and or television images on photographic paper or the like. Such types of printers are favored since they require no thermal head or ink ribbon, and may operate on low levels of electricity. In addition they may be substantially small in size and low in cost.
One such sublimation type video printer is disclosed in Japanese Patent Application (First Publication) No. 4-300587. Such a conventional type of sublimation printer will be explained in detail with reference to FIGS. 14 and 15. As may be seen in FIG. 14, a laser sublimation type color video printer (hereinbelow: printer) 1 receives a cassette 3 containing photographic paper 50'. The printer 1 includes a planar base 4 for printing on a chassis 2, the chassis 2 is covered by an outer case 2a. A discharge slot 2b is provided in the front face of the outer case 2a and, behind the discharge slot 2b, a feed roller 6a is provided, driven by a motor 5. The feed roller 6a contacts a pressure driven roller 6b such that the photographic paper 50' may be discharged from the printer 1 between the rollers 6a, 6b. The printer 1 further includes a head driving circuit substrate 7 connected to a head assembly 10P which is disposed on the planar base 4. The substrate 7 and the head assembly 10 are connected by a flexible wire harness 7a.
Referring now to FIGS. 15 and 16, the head assembly is provided with dye tanks (11Y (yellow), 11M (magenta), 11C (cyan)) 11, accommodating solid sublimation type dyes 12, of each of the above-noted primary colors. The dyes 12 may be in solidified powder form, for example. A dye passage 15 (15Y, 15M, 15C) connects between each of the tanks 11 and vaporizing sections 17 over a wear-resistant protective layer 13 of the head assembly 10P. The protective layer 13 is made of a high strength material and is located at the lower side of a head base 14 made of glass, transparent ceramic, or the like. The dye passage 15 allows passage of the dye 12 as liquefied dye 12' after heating by heating units 16D (FIG. 15), which comprise a resistor provided at the lower surface of the head base 4. The liquefied dye 12' from each of the dye passages 15 is brought to the vaporizing sections 17. There may, for example, be three vaporizing sections 17Y, 17M and 17C, one for each of the primary colors yellow, magenta and cyan. A laser beam source (i.e. a semiconductor laser)18 is mounted above the head base 14 on a mounting stand 19. Vaporizing pores 17a of the vaporizing sections 17 are irradiated by laser beams L generated at the laser sources 18.
As best seen in FIG. 15, each of the vaporizing sections 17 comprise a plurality of pores 17a in each of which an upper transparent insulation layer 20' is provided at a lower side of the head base 14 atop a light-heat conversion layer 21' and a lower adhesion layer 23'. The light-heat conversion layer 21' absorbs light from the laser beam L and converts same into heat, while the adhesion layer 23' has glass beads 22' inset therein for carrying vaporized dye 12" vaporized by the laser beam L at each vaporizing pore 17a. The transparent insulation layer 20' is made of a clear PET resin, for example, and the light-heat conversion layer 21' is formed by applying a binder and fine carbon particles to the lower side of the transparent insulation layer 20' Glass beads 22' are selected with a size from 5-10 microns in diameter. The heating units 16 are active to allow the solid dye 12 to liquefy and be maintained as liquefied dye 12' and to flow down to be held at the glass beads 22' to be converted to vaporized dye 12" according to irradiation of the vaporizing section 17 by the laser beam L.
Sheets of the photographic paper 50' are drawn singly out of the cassette 3 between the planar base 4 and the head assembly 10P to be fed to the rollers 6a, 6b. The head assembly 10P is biased against the plane base 4 under a light load (approx. 50 g) by load applying springs 9, as seen in FIG. 14.
A plurality of laser sources 18 for each of the colors Yellow, Magenta and Cyan (hereinbelow: Y, M, C) are aligned at the head assembly 10P in three rows to perform heating and liquefaction respectively for the dyes 12Y, 12M and 12C. The dyes 12 in each of the dye tanks 11Y, 11M and 11C are heated to the melting point by the heating elements 16 and quantitatively supplied to each pore 17a of the plurality of vaporizing portions 17Y, 17M, 17C via the passages 15. The dye 12 may move from the tanks 11 to the glass beads 22' via a simple capillary effect.
For printing, when the photographic paper is positioned between the rollers 6a, 6b, a signal is sent to the head portion for each one line of an image to be printed and for each single color laser beams L are generated accordingly at the laser sources 18 which are then converted to heat at the respective light-heat converting layers 21' such that an appropriate amount of liquefied dye of each color Y, M and C, is held at the glass beads 22' to be vaporized by the applied heat to be imprinted successively in the order of Y, M and C to a dye receiving layer 50'a at the surface of the photographic paper 50'. The imprinted photographic paper 50' is then fed between the protective layer and the planar base 4 to result in a finished color print.
FIG. 18 shows a conventional type of photographic paper utilized in such a laser sublimation type printer 1 as described above. As may be seen, the photo paper 50' is a laminate comprising of a dye receiving surface layer 50'a, a light-absorbing layer 50'e, a polypropylene layer 50'b, a base paper layer 50'c and a polypropylene layer 50'd. According to this, the light-absorbing layer 50'e of the photographic paper 50' absorbs a portion of the light from the laser source 18 and converts it to heat which heats the dye receiving surface layer 50a to aid the vaporized dye 12" in forming a thermal imprint on the dye receiving surface layer 50a.
As seen in FIG. 16, the head portion 10P of such a laser sublimation type printer 1 may have an elongate pore 17b formed along one side thereof. This elongate pore 17b allows irradiation of the photographic paper by a second laser Lo for removing discoloration caused by the presence of a light absorbing agent present in the light absorbing layer 50'e of the photographic paper 50'. That is, the agent present in the light absorbing layer 50'e gives the photographic paper 50' pale tint, irradiation by the laser beam Lo whitens the light absorbing agent to produce a sharper more attractive image on the photographic paper 50'.
However, according to such a conventional laser sublimation printer arrangement, since the light-heat converting layers 21' must be formed by application of the binder and carbon particles to the transparent insulation layer, if a thickness of the layer becomes greater than 1 micron, heat capacity becomes too large (specific heat is generally 1.3J/g.degree.C. which is substantially high) and thermal conduction efficiency is reduced (i.e. 0.15w/m.degree.C.), also, the diffusion speed of heat becomes slower. Therefore, when light energy distribution of the laser beam is non-uniform, such as a gaussian distribution or the like, heat conversion Follows this distribution and it becomes difficult to imprint colors uniformly. Also, since the dyes 12 are brought to the glass beads 22' by a capillary phenomenon, and the sizes of the glass beads 22' may vary slightly, it is difficult to assure that a uniform amount of dye is brought to each vaporizing section 17 and for this reason also, uniformity of color is difficult to assure.
In addition, the light-heat converting layer 21' itself is subject to destruction due to generated heat and the PET resin material of the insulation layer 21' is apt to incur thermal damage at around 140.degree. C. Also, the area of the light-heat converting layer 21' is larger than an irradiation area of one spot of light from the laser source 18 and an imprint area of the dye 12 and an energy efficiency of heat imprinting is degraded as excessive heat is lost.
Further, since the glass beads 22' are used as the holding layer for retaining the liquefied dye 12' prior to vaporizing, an adhesion layer 23' must be provided and the problem of heat resistance is incurred. That is, while the supply of liquefied dye 12' to the glass beads 22' depends on the diffusion speed of the dye 12 itself, it is impossible to supply the dye 12 to the glass beads 22' at significantly high speeds since the speed of supply varies according to operating influences and the influence of the respective laser sources 18.
Also, in order to maintain a high resolution for assuring good image quality, the vaporizing sections 17 must be provided in rows and spaced about 30 microns apart. This limits material which can be used for the protective layer 13 and incurs high production costs in manufacture for etching and adhesion technique, etc. It is also noted that, according to the conventional structure, a separate, dedicated laser source is required For operating in the elongate pore 17b for irradiating the light-absorbing agent.
Thus, it has been required to provide a sublimation type laser color video printer in which the above drawbacks may be alleviated.